32§ Journal of conchology. 



VARIATION IN THE SHELLS OF THE MOLLUSCA. 



By PHILIP BROOKES MASON, J. P., F.L.S., etc., 



President of the Conchological Society of Great Britain 



AXD Ireland. 



Being the Presidential Address delivered to the Society, Sept. i6, 1893. 



I must commence with an apology for selecting variation 

 as the subject for this evening's address, especially after the 

 demonstrations to which we had the privilege of listening last 

 year in Manchester, when Dr. Norman showed us part of the 

 riches of his vast collections — collections which enable him to 

 survey the shell, if not from ' China to Peru,' at least from that 

 portion of the earth's surface, viz., the whole of the Pala^arctic 

 Region, which is best known, most completely explored, and in 

 which the relationship of the indigenous species and varieties 

 have been most thoroughly investigated. 



My own horizon is, indeed, a much more humble one, 

 being bounded by the limits of the British Seas. 



The theme, although well worn, is of so great and, if we 

 extend our enquiries beyond the limits of the MoUusca to the 

 Vegetable and remainder of the Animal Kingdom, of so 

 absorbing an interest, lying as it does at the root of so many of 

 the problems of Biology, that I hope it may not weary you too 

 much if I devote a short time to a glance at some of the aspects 

 of variation in this class. 



Before we can speak of variation or varieties, we must have 

 a standard from which the individual can diverge in some way 

 or another. This leads me directly to the question — What is a 

 species ? It must not be forgotten that the species itself is an 

 arbitrary abstraction, no such thing existing in nature. It is a 

 convenience to class many individuals, which possess certain 

 features in common, as one species, although if these individuals 

 be minutely examined, no two specimens will be found to be 



J.C., vii., Jan. 1S94. 



